Automated material handling systems (AMHS) have been widely used in semiconductor fabrication facilities (also termed as FABs) to automatically handle and transport groups or lots of wafers between various processing machines or tools used in chip manufacturing. A typical FAB may include a plurality of process bays including processing tools (e.g., a process tool) and wafer staging equipment which are interconnected by the AMHS.
Each bay may include a wafer stocker, which includes multiple bins for temporarily holding and staging a plurality of wafer carriers during the fabrication process. The wafer carriers may include standard mechanical interface (SMIF) pods which may hold a plurality of wafers, or front opening unified pods (FOUPs) which may hold larger wafers. Stockers generally include a single mast robotic lift or crane having a weight bearing capacity sufficient for lifting, inserting, and retrieving a single wafer carrier at one time from the bins. The stocker holds multiple SMIF pods or FOUPs in preparation for transporting a SMIF or FOUP to the loadport of a process tool.
A semiconductor FAB may include numerous types of automated and manual vehicles for moving and transporting wafer carriers throughout the FAB during the manufacturing process. These may include for example automatic guided vehicles (AGVs), personal guided vehicles (PGVs), rail guided vehicles (RGVs), overhead shuttles (OHSs), and overhead hoist transports (OHTs). An OHT system automatically moves OHT vehicles that carry and transport wafer carriers, such as SMIF pods or FOUPs holding multiple wafers, from a processing or metrology tool (e.g., process tool) or a stocker to the loadport of another tool or other apparatus in the FAB. The OHT system may be used to transport vehicles within each bay (intra-bay) or between bays (inter-bay). The OHT system also moves empty vehicles (i.e. without a wafer carrier) to the tool loadport or other apparatus for receiving and removing empty or full SMIF pods or FOUPs that may contain wafers for further transport and/or processing in other tools.
Handling and transport of wafers in correspondingly larger and heavier FOUPS creates efficiency challenges for the AMHS to maintain expedient wafer flow between process tools in the semiconductor FAB. In addition, construction of large Giga FABS with potential capacities to handle processing of more 100,000 wafers per month creates additional demands. These challenges and demands include efficient use of floor and overhead space in the FAB and reducing bottlenecks or vehicle traffic jams due to vehicle failures and/or damage.
Accordingly, an improved system and method for handling wafer transport in a semiconductor FAB is desired.